public double MinimumResolution {get;}

var dsCount = terrain.GetDataSourceCount();
IReadOnlyList<ArcGIS.Core.Data.Analyst3D.TerrainDataSource> dataSources = terrain.GetDataSources();
foreach (var ds in dataSources)
{
  var dsName = ds.DataSourceName;
  var surfaceType = ds.SurfaceType;
  var maxResolution = ds.MaximumResolution;
  var minResolution = ds.MinimumResolution;
}